Ozone or chlorine is typically used in conventional water and sewage treatment. However, industrial wastewater, recycled water, and so on, for example, may contain persistent substances that are not decomposed by ozone or chlorine. Removal of dioxins, dioxane, and so on is particularly problematic.
A method of removing persistent substances by combining ozone (O3) with hydrogen peroxide (H2O2) or ultraviolet light in order to generate hydroxyl radicals (OH radicals), which are more highly active than ozone or chlorine, in water to be treated is in partial use, but due to extremely high apparatus costs and running costs, this method has not become popular. Hence, a method of removing persistent substances efficiently by applying OH radicals generated through electrical discharge directly to the water to be treated has been proposed.
More specifically, a water treatment apparatus that treats water to be treated by applying a pulse voltage between a high voltage wire electrode and a cylindrical ground electrode surrounding the high voltage wire electrode in order to form a streamer discharge, and supplying the water to be treated in droplet form into a streamer discharge space from above using an ejection nozzle has been proposed. According to this water treatment apparatus, OH radicals, which have a short life, can be applied efficiently to the water to be treated (see PTL 1, for example).
A water treatment apparatus for treating water to be treated by disposing a pair of electrode plates that oppose each other vertically at an incline and pouring the water to be treated onto the lower electrode so that the water to be treated flows down over the lower electrode, whereby a barrier discharge is formed between the electrodes, has also been proposed. With this water treatment apparatus, the water to be treated can be treated efficiently using a simple configuration (see PTL 2, for example).